On Mon, Mar 11, 2013 at 12:28 PM, Oleg Nesterov <o...@redhat.com> wrote: > On 03/11, Kees Cook wrote: >> >> When the new signal handlers are set up for a fork, the location of >> sa_restorer is not cleared, leaking a parent process's address space >> location to children. This allows for a potential bypass of the parent's >> ASLR by examining the sa_restorer value returned when calling sigaction(). > > I don't understand. > > fork() should not change restorer/etc, and the child has the same address > space anyway. There is no any leak and the patch can't make any difference > in this case because flush_signal_handlers() is not called by fork().
I probably failed to explain this correctly. From the perspective of what should be considered "secret", it only matters across the exec, not the fork (since the VMAs haven't changed until the exec). But the info leak is easy to see, and this patch fixes it. As you say, since other things were reset, so should sa_restorer. > >> @@ -485,6 +485,9 @@ flush_signal_handlers(struct task_struct *t, int >> force_default) >> if (force_default || ka->sa.sa_handler != SIG_IGN) >> ka->sa.sa_handler = SIG_DFL; >> ka->sa.sa_flags = 0; >> +#ifdef __ARCH_HAS_SA_RESTORER >> + ka->sa.sa_restorer = NULL; >> +#endif > > However, exec sets SIG_DFL but keeps ->sa_restorer, so probably this > patch makes sense anyway. > > Oleg. > -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
